...to build up a .45ACP AR45. Has anyone got any experience with this platform? The questions I have are:

1: Does it in fact require a different spring in the buffer than the 9mm or 5.56 NATO?
2: Does the .45ACP range get affected by the barrel length?
3: Are there any issues with using +P ammo in the AR platform?

Any experience with this would be greatly appreciated as this will be my first AR "build".

I will be building almost exactly like the one pictured (short gas block w/flip up BUIS) as my sub/fun gun.

Thanks in advance for everyones help!

__________________“The things that will destroy America are prosperity-at-any-price, peace-at-any-price, safety-first instead of duty-first, the love of soft living, and the get-rich-quick theory of life.” -Theodore Roosevelt

"The course of history shows that as a government grows, liberty decreases." -Thomas Jefferson

"You should never underestimate the predictability of stupidity. -Bullet Tooth Tony

I have an Oly 45 upper on a CavArms MkII lower. The CavArms lower ($125) is specially designed to take both regular M16 magazines (for 556 uppers) and 45 Greasegun magazines with Hanh magazine adapter.

1) The CavArms polymer lower does require a heavy 8oz buffer, otherwise, full auto pistol carbines can use it to increase reliabiliy.

2) I've found that the 25yd zero with 45acp is close to the 100yd PoI. If you have a 25yd zero, at 7yds the bullets PoI is halfway up the front sight post.

3) none, the Oly upper is very strong and one of the arfcom guys shoots .45 Super out of his.

With the 16" barrel, you don't really need a flashhider, and I have a simple thread protector on the end of mine. I got it from a guy on eBay for $10 (5/8"id x24 tpi, 5/8" long).

One last thing about the CavArms polymer lower, if you ever f*** it up, they'll replace it for $30. Plus you can put a regular 223/556 upper on it and shoot rifle ammo if you ever change your mind.